In the testing of liquids and particularly engine oils it is important to determine the viscosity of the oils to assure proper lubrication of an engine. If the engine oil is too thick or too thin proper lubrication of the engine cannot be assured. In some cases oil which has been used in an engine is removed or part thereof for appropriate testing to determine the viscosity. In other cases a customer may desire to know the quality (viscosity) of new oil he is buying in large volume. This is particularly true where there are large fleets of vehicles and oil is bought in large drums for use in the engines of the fleet of vehicles.
There have been many attempts to test the viscosity of motor oil and one in particular that has been used is known as a capillary tube viscometer. This is generally an elongated glass tube with various bends and in certain cases visual marks therein so that as the oil passes between one mark to the other the time it takes may be measured and from that certain charts and tables can be used to calibrate the viscosity of the oil.
There are disadvantages to the visually read capillary viscometer. With concentration, the very best possible visual reading would probably be accurate to within +0.05 seconds. In actuality when several tubes are run simultaneously by an experienced technician, a visually timed accuracy on the order of +0.1 seconds would be expected.
It is desirable that the test for viscosity of the oil should be run at temperatures up to 210.degree. F. This requires that the capillary tube be emersed in a hot oil bath. Therefore the visual inspection which must take place through the heated fluid or liquid within which the capillary tube is emersed can be distorted and confuse readings in multiple tube installations. A true reading is somewhat difficult to achieve.
With fiber optics as described in this invention it is possible to accurately and automatically read and time the start and stop of oil running pass certain points in a capillary tube viscometer.